Boric acid-methyl polysiloxane composition



Patented July 7, 1953 ,Y .1;-

This invention is concerned with novel polysiloxane compositions andparticularly relates to a composition of matter having unique propertiesobtained by effecting reaction between boric acid and tetramethyldisiloxane dial-1,3.

The compositions herein described have unique properties depending onthe temperatures to which they are subjected. I have found that when oneeffects reaction between boric acid and tetramethyl disiloxane dio1-1,3,there is obtained a composition which at or around normal temperaturesof the order of about 25 to 35 C. resembles a thin starch paste inappearance. However, if the mixture is stirred and warmed to about 50-55C. or higher, the mixture congeals rapidly forming a mass resemblingbouncing putty described in Wright Patent 2,541,851, issued February 13,1951, and assigned to the same assignee as the present invention. Thematerial resembles the bouncing putty described in the aforesaid patentin that it can be deformed by the slow application of pressure. However,if dropped on a hard surface it bounces as a rubber ball. In thetemperature range of approximately 55 C. it possesses the propertiescommonly associated with bounc- -.-,".2,644,so5- I BORIC ACID-METHYLrttrsmbxmg ,ooMPosI'rroN I J ,Martin, Lenox, Mass., ;assig'nortd-.Gen-;

ny, weorpqratiomof New f ing putty. However, on cooling, the compositionloses its putty-like properties and is converted to a starch-likesolution or thin paste again which is entirely contrary to the resultsobtained when similar temperature changes are applied to the bouncingputty described in the aforesaid Wright patent. If the composition isagain heated, its. physical form changes back to something resemblingagain the bouncing putty. This process of heating to cause congealingand cooling to melt the composition can be repeated a number of times.

The tetramethyl disiloxane diol-1,3 may be prepared in accordance withthe method described and claimed in Lucas et a1. application, Serial No.149,886 filed March 15, 1950, now U. S. Patent 2,600,307, issued June10, 1952, and assigned to the assignee of the present invention.

The proportion of tetramethyl disiloxane diol- 1,3 (hereinafter referredto as diol) to boric acid may be varied within limits to obtain thedesired composition. Generally, on a Weight basis, for each part ofboric acid used I may employ from 2.5 to 3.5 parts of the diol.Generally, I have found that best results are obtained when from 2.8 to3.0 parts of tetramethyl disiloxane diol-1,3 is mixed with 1 part ofboric acid and the mixture warmed slightly or ground together to obtaina thin starchy paste.

In order that those skilled in the art may better v JplicatibhMziilS;1951i x1,F rm- 54? 1 Claim. (01. 260 48.5 f

2 understand how the present invention may be practiced, the followingexample is given by way of illustration and not by way of limitation.All parts are by weight.

Emample A mixture of 8.3 parts tetramethyl disiloxane dio1-1,3 and 2.96parts boric acid was placed in an open vessel and the mixture heatedslightly. As soon as a few of the tetramethyl disiloxane diol- 1,3crystals had melted, the entire mass became a thin solution with Whatappeared to be some undissolved boric acid suspended in the solution. Itwas surprising to find that such a, mixture was fluid at roomtemperature when the tetramethyl disiloxane diol melts at 67-68 C. andboric acid melts at 185 C. with decomposition.

The mixture was warmed to about 50 C. on a steam bath and stirred.Almost immediately the mass formed a stiff putty-like composition. Thisputty-like material bounced when dropped onto a hard surface, yet couldbe readily deformed by the application of slow pressure. On allowing themass to cool, it melted when the temperature reached about 35 C. to givea thin starch-like paste or solution. On reheating the starch-like massto about 55 0., gelation or congealing again occurred. On working theputty-like material and cooling to 37 C., the gel or putty becamestringy and again softened and the starch-like solution again formed.This process of heating to cause gelation or formation of the putty andcooling to form a starch-like paste was repeated several times. Afterabout six times, the last time the gel Was formed, cooling failed togive the starch-like solution. Instead, .a somewhat crumbly massremained. After heating 16 hours at 50 0., a crumbly, dry materialresulted. This was ground in a mortar with 1.5 ml. water. Again astarch-like paste formed which on heating to 55 C. congealed as before.On stirring and cooling to room temperature, a starch-like paste wasagain formed. This showed that the loss of reversibility of the systemafter repeated heating and cooling operations was, in .part, due to theloss of water. .When sealed in a glass tube, the composition maintainedits reversibility without change through more than 12 cycles of heatingand cooling.

The composition described above will tolerate certain materials inaddition to the boric acid and tetramethyl disoloxane diol-1,3. Thus,the addition of small amounts of water results in a thinner starch-likepaste on cooling to 45 C. after the I mixture has been warmed to C. togive a congeal ed rather stiff putty. The addition of 1 part diethyleneglycol to the composition described in Example 1 and thereaftersubjecting the mixture to warming to around 55-60 C., gave again to abouncing putty. On cooling to 40 C., an opalescent solution was 'formed.Other materials which can be added include various pigments such astitanium dioxide, lithopone, etc; glycerine, which when added to thecomposition of matter described in the Example gives an irreversible gelwhen the mixture is heated.

The composition of matter described herein may find use as a controldevice wherein the change in the physical state of the compositioncaused by changes in temperature may be able to actuate electricalcontacts, and thus control opening and closing of the contacts.

What I claim as new and desired to secure by Letters Patent of theUnited States is:

The method which comprises (1) forming a mixture of ingredientscomprising, by weight, 1 part boric acid and from 2.5 to 3.5 partstetramethyl disiloxane dial-1,3, and (2) warming the mixture ofingredients slightly to produce a composition which at normaltemperatures of about to resembles a thin paste but at temperatures offrom to C. congeals to a putty-like composition.

ROBERT W. MARTIN.

References Cited in the file of this patent UNITED STATES PATENTS NumberY Name Date 2,258,218 Rochow Oct. '1, 1941 2,431,878 McGregor Dec. 2,1947 2,600,307 Lucas June 10, 1952

